1. Field of the Invention
The invention relates to cathode ray tube displays and more particularly to gain controls for the deflection systems of cathode ray displays of the phosphor penetration type employing rapidly selectable high anode or acceleration voltages and providing improved color displays.
2. Description of the Prior Art
Penetration phosphor cathode ray tubes are attractive for use in displays wherein their bright color producing capabilities permit the presentation of complex data in semipictorial forms quickly interpretable by the viewer. They are additionally attractive for use in such information displays, including displays for air traffic control, navigation, radar, and the like systems, because they provide images with uniform high resolution and good contrast.
A conventional penetration phosphor cathode ray tube has a viewing screen which uses controlled penetration of electrons into a series of phosphor layers for producing therein light of a corresponding series of colors. For example, the screen may include two or more different phosphor layers, each very thin, uniform, and separated by a transparent dielectric layer. When the electron beam is driven by a relatively low voltage, the energy of the electrons is not sufficient to penetrate the dielectric barrier layer; only the phosphor of the first layer is excited and only its color is produced. At higher electron beam voltages and correspondingly higher electron energies, the phosphors of both of the first and second layers are excited, the intensity of the color contribution by the second layer phosphor increasing as the electron beam energy is increased.
Full use may be made of the penetration phosphor characteristics in providing a variable color display while using only one electron beam simply by controlling the voltage on the beam acceleration electrode adjacent the focusing electrode. With red and green emitting phosphors, successive changes in the beam acceleration voltage generate distinct colors; for example, red, orange, yellow, or green may thus be generated. Only one suitably controlled electron gun is required and the apertured masks of prior art color television tubes are eliminated along with other features undesirable for use in fast high resolution information displays. A further understanding of the construction and operation of such penetration phosphor displays is found in the following Sperry Corporation U.S. patents:
S. F. Ignasiak, U.S. Pat. No. 3,939,377 for "Penetration Phosphors and Display Devices", issued Feb. 17, 1976, PA1 C. D. Lustig, J. B. Thaxter, U.S. Pat. No. 3,946,267 for "Plural Filter System Cooperating With Cathode Ray Display with Lanthanum Host Phosphor Emissive in Two Colors," issued Mar. 23, 1976, and PA1 S. F. Ignasiak, U.S. Pat. No. 4,071,640 for "Penetration Phosphors for Display Devices," issued Jan. 31, 1978.
In the penetration phosphor kind of cathode ray tube display, where the anode beam acceleration voltage is changed over wide ranges, the effective stiffness of the electron beam changes widely, and a proportionately greater beam deflection current is required as the electron beam acceleration voltage is increased in order to deflect the beam through a predetermined horizontal or vertical deflection angle. While the existence of this problem appears to have been recognized in the past, continuous and instantaneous gain changing was not satisfactorily accomplished even by the use of the discrete analog switch-resistor control matrix, an arrangement inprecise and not effective in the very rapid display of data. Furthermore, relatively precise anode power supply regulation was required, since the effects of any power supply ripple present were not otherwise eliminated.